FIG. 1 illustrates a top drive system 10 which is structurally supported by a derrick 11. The top drive system 10 has a plurality of components including a top drive 14, (shown schematically) a main drive shaft 16, a motor housing 17, a drill string 19 and a drill bit 20. The components are collectively suspended from a traveling block 12 (moved by a “drawworks”—not shown) that allows them to move upwardly and downwardly on rails 22 connected to the derrick 11 for guiding the vertical motion of the top drive system components. Reactance to torque generated during operations with the top drive and its components (e.g. during drilling) is transmitted through the rails 22 to the derrick 11.
The main drive shaft 16 extends through the motor housing 17 and connects to items below the shaft (“stem” or “shaft” can include stems and shafts). The main drive shaft 16 may be non-threadedly connected to an upper end of an IBOP assembly 24 which is the first in a series of items and/or tubular members collectively referred to as the drill string 19. An opposite end of the drill string 19 is threadedly connected to a drill bit 20.
During operation, a motor 15 (shown schematically) encased within the motor housing 17 rotates the main drive shaft 16 which, in turn, rotates the drill string 19 and the drill bit 20. Rotation of the drill bit 20 produces a wellbore 21. Drilling fluid pumped into the top drive system 10 passes through the main drive shaft 16, the drill string 19, the drill bit 20 and enters the bottom of the wellbore 21. Cuttings removed by the drill bit 20 are cleared from the bottom of the wellbore 21 as the pumped fluid passes out of the wellbore 21 up through an annulus formed by the outer surface of the drill bit 20 and the walls of the wellbore 21. Typical elevators 29 are suspended from the top drive system 10 to perform “pipe tripping” operations as will be explained in more detail.
A variety of items can be connected to and below the main drive shaft 16; for example, and not by way of limitation, the items shown schematically as items 24 and 26 which, in certain aspects, and not by way of limitation, may be an upper internal blowout preventer 24 and a lower internal blowout preventer 26. In other systems according to the present invention the item 24 may be a mud saver apparatus, a load measuring device, a flexible sub, or a saver sub. A connection assembly 40 can non-threadedly connect the item 24 to the main drive shaft 16. The main drive shaft 16 may be a drill stem or a quill.
In typical top drive drilling operations, the top drive elevators 29 are set to have a pipe handler (explained below) orientated in one rotational direction to trip pipe (move the drill string into and out of the wellbore), which limits the travel of the elevators 29. This allows the elevators 29 to clear a racking board and/or parts in relation to the racking board, and this may include parts of the derrick 11. Such orientation allows the top drive 10 to travel up to or down from the racking board 42 and crown (top of the derrick 11) without the possibility of interference between the top drive pipe handling equipment and other items. This also allows the elevators 29 and associated pipe handling equipment to extend out as close as possible to the derrick man/racking board without of interference between components.
When the elevators 29 are used to move the drill string 19 into and out of the well, certain components of the top drive experience metal to metal contact by reason of the axial load of the drill string 19 on the elevators 29. If the top drive motor 15 (shown schematically) rotates the main drive shaft 16 when substantial axial loading is applied to the elevators 29, there is risk of damage to the top drive because of metal to metal contact between a “link load collar” that transfers load on the elevators 29 to the housing 17 and to the main drive shaft 16, and the main drive shaft.
There exists a need for an automatic system to determine whether there is axial loading in the elevators to automatically prevent rotation of the main drive shaft or “quill” during such times as axial loading is applied to the elevators.